1. Field of the Invention
The present invention relates to an optical semiconductor device in the form of an optical semiconductor device formed from a plurality of light-emitting diodes arranged in set intervals which displays specific data by ON and OFF combinations, and, in particular, to an optical semiconductor device which can display data clearly, irrespective of changes in the amount of incident external light or of the position of a person viewing the display.
2. Description of the Prior Art
Conventionally, an optical semiconductor device as a display unit formed from light-emitting diodes in a plurality of locations arranged in matrix form can display specified data when the light-emitting diodes are set to ON or to OFF. At the present time, such an optical semiconductor device is widely used both indoors and outdoors as a display device such as a display panel in which a specific number of light-emitting diodes are combined.
For example, these display devices are installed on the shoulder of a highway to provide road data for drivers, or the like, or are installed in railway stations to provide passengers with a guide to the departure and arrival times of the trains. FIG. 1A is a plan view of an optical semiconductor device 1 used as a display unit for a conventional display device. This display device 1 is fabricated from nine light-emitting diodes 2.
The light-emitting diodes 2 are arranged in a peripheral member 3 in a systematic matrix form. A resin 4 is filled between the light-emitting diodes 2 of the peripheral member 3 to secure the light-emitting diodes 2 in the peripheral member 3. FIG. 1B is a sectional view along a line A--A' of the optical semiconductor device 1 of FIG. 1.
For example, a plurality of optical semiconductor devices 1 are combined and arranged in one plane, for example, to form a display device for information in a railroad station as stated above. FIG. 2A is a plan view of a display device 7 used as a display unit, formed by combining a plurality of conventional optical semiconductor devices 1. FIG. 2B is a sectional view along a line B-B' of the display device 7 shown in FIG. 2A.
In the display device 7 shown in FIG. 2A, for example, in the case of an outdoor installation, the sunlight shines directly onto the light-emitting diodes 2, which are, specifically, LED lamps. In this case, it is difficult to distinguish whether the LED lamps 2 are illuminated or extinguished, so, as a result, there is the problem that the displayed data cannot be understood. Conventionally, to solve this problem, a louver 5, for example, is provided in one part of the peripheral member 3 of the optical semiconductor device 1, as shown in FIG. 1B, so that external light does not shine directly onto the LED lamp 2.
As a result, when the LED lamp 2 is extinguished it is difficult for external light to be directed onto the LED lamp 2 or the resin 4 and there is a large difference between the amount of light from the light-emitted diode 2 when the light-emitting diode 2 is lighted and the amount of light from the resign 4 in the optical semiconductor device 1 when the diode 2 is extinguished. Specifically, the clarity of contrast in the total optical semiconductor device 1 is large. Accordingly, a good display is possible.
However, the optical semiconductor device 1 is arranged in matrix form to form the display device 7, and when a long louver 5 is provided in the peripheral member 3 to restrain the effect of external light, the visibility in the display device 1 in the vertical direction in particular is lost. For this reason, there are cases where the louver 5 must be short, depending on the location at which the display device 1 is installed and the magnitude of the display portion. For example, in the case of a display device utilizing the optical semiconductor device shown in FIG. 1A and FIG. 1B, there are occasions when the LED lamp 2 is difficult to see when viewed from the B direction. For this reason, the louver 5 must be short.
In such a case, the louver 5 cannot block out a sufficient amount of external light, and when the LED lamp 2 is illuminated or extinguished, the contrast in a specific direction is poor.
In addition, the resin 4 used for setting the light-emitting diode 2 in the peripheral member 3 normally has a low viscosity. Specifically, in the case where a high viscosity resin is used, it is run into the perimeter of the light-emitting diode 2 and cured to avoid the production of cavities at the periphery of the light-emitting diode 2. However, when a low viscosity resin is used a mirror-like surface is formed. As a result, external light directed onto the surface of the resin 4 is reflected in a specific direction so that it is impossible to understand the display data.
As a countermeasure for such inconveniences, the reflection of external light from the LED lamp 2 can be restrained to a certain extent by changing the shape of the LED lamp 2. However, no effective countermeasure has as yet been found for the resin problem.
As explained above, in a conventional optical semiconductor device 1 utilizing a display device which is mainly for outdoor application, a long louver 5 for blocking out the light provided to the peripheral member 3 cannot be used, therefore external light is strongly reflected from the surface of the resin 4 which is filled into the peripheral member 3. This gives rise to the drawback that the optical semiconductor device, specifically, the display device, is difficult to see.